I. Field of the Invention
This invention relates to diamond drag bits for drilling boreholes in earthen formations.
More particularly, this invention relates to diamond drag bits having supported Stratapax type polycrystalline cutter studs strategically inserted and positioned in the face of the drag bit body.
II. Description of the Prior Art
A number of prior art patents reflect the state of the art relative to the use of diamond insert studs in diamond drag bits.
U.S. Pat. No. 4,265,324 assigned to the same assignee as the present invention teaches the use of insert studs that are counterbored in the face of a drag bit. The counterbore relieves the upper portion of the bored hole formed in the face of the bit body. The hole is formed to receive the shank of the insert stud.
The counterbore serves to clear the bottom edge of the diamond cutting face of the insert. The stud portion behind the cutting face of the insert is then supported by the bit face depending upon the depth of the counterbore.
While the novel means to support the insert stud is fairly satisfactory, the counterbore caused turbulent flow of the cooling and cleaning fluid passing by each of the diamond inserts during operation of the bit in a borehole.
The use of a counterbore to add strength to the stud cutter substantially reduced the extension of the cutter below the bit body face, thereby reducing the depth of cut or the plastic deformation of the rock reducing the drill rate.
U.S. Pat. Nos. 4,244,432 and 4,351,401 are examples of other diamond drag bits that utilize stud type diamond inserts pressed into insert holes formed in the face of the drag bit.
The foregoing patents are disadvantaged in that the cutting end of the studs are unsupported and are vulnerable to fracturing just above the face of the bit.